1. Field of the Invention
The present invention relates to an optical lens driving technology, and more particularly, to a piezoelectrically driven optical focusing device.
2. Description of the Prior Art
Optical systems and actuators for use in cellular phones and cameras nowadays are structurally simple and small-sized to conform with the trend of miniaturization. A piezoelectric actuator has advantages, such as small size, large output, low power consumption, noiseless, and high compatibility. Hence, a piezoelectric actuator is a constituent part of a digital camera or a camera phone for driving an optical lens therein and providing the zoom-in function and zoom-out function. Therefore, a piezoelectric actuator is important to any optical systems or related products.
U.S. Pat. No. 7,099,093 disclosed a small-sized lens module as shown in FIG. 1, wherein a piezoelectric actuator 100 drives a transmission wheel 101 for positioning a rotating threaded shaft 102, thus allowing a lens 103 to move to and fro. Given the moment arm formula M=r×F, miniaturization of the transmission wheel 101 bring about a decrease of overall volume, but the piezoelectric actuator 100 has to work harder and ends up with an increase of power consumption. If the transmission wheel 101 is enlarged, the overall volume of will increase to the detriment of miniaturization.
U.S. Pat. No. 5,225,941 disclosed a driving device as shown in FIG. 2, comprising a multilayer piezoelectric actuator 104, a leaf spring 105 for generating preload, and a lens 106, wherein an inputted driving signal causes the lens 106 to forward or backward. However, the multilayer piezoelectric actuator 104 has to comprise multilayer piezoelectric plates for the sake of considerable displacement and exertion. Accordingly, it is difficult to thin out the driving device.
U.S. Pat. No. 6,710,950 disclosed a piezoelectric actuator for use in an optical system of a digital camera. As shown in FIG. 3, a piezoelectric actuator 109 is externally coupled to a sleeve 108 of a lens unit 107. The piezoelectric actuator 109 comprises a circuit board 110, a plurality of piezoelectric plates 111, and a plurality of engagement pads 112. The piezoelectric plates 111 are equidistantly spaced and formed on the inner surface of the circuit board 110. The engagement pads 112 are coupled to the piezoelectric plates 111 respectively. Applying a voltage to the piezoelectric plates 111 disposed on the outer circumferential surface of the lens unit 107 allows the piezoelectric plates 111 to generate a surface wave which, in turn, causes the engagement pads 112 to push the lens unit 107 synchronously, and in consequence the lens unit 107 undergoes axial displacement relative to the sleeve 108, thus achieving optical focusing of the digital camera. However, the piezoelectric actuator 109 disclosed in U.S. Pat. No. 6,710,950 is expensive and difficult to assemble, because of a plurality of piezoelectric elements used, not to mention that control over synchronous displacement of piezoelectric elements is unlikely to be precise. Moreover, the length of the sleeve 108 is displacement-dependent, and thus the sleeve 108 will have to be rather long to the detriment of miniaturization in pursuit of great displacement.
U.S. Pat. No. 6,961,193 disclosed a driving device for driving a lens. As shown in FIG. 4, the driving device comprises a piezoelectric plates 113, a lens 114, and a weight 115. The piezoelectric plates 113 generates an inertial force for driving the lens 114 forward or backward. However, to generate the inertial force, the piezoelectric plates 113 has to be outwardly provided with the weight 115, thus increasing the diameter and mass of the driving device.
Accordingly, an issue calling for an urgent solution involves developing an optical focusing device having advantages, such as great driving torque, small size, structurally simple constituent components, well-built structure, easy to fabricate, and convenient to assemble, with a view to solving the existing drawbacks of the prior art.